The present invention relates to a piston ring member. More particularly, the invention relates to a piston ring member suitable for use in reciprocating internal combustion engines, such as a compression ring member or an oil ring member, for instance, a side rail member for use with oil rings.
Modern internal combustion engines are designed to produce a greater power output at higher speeds, and demands upon the performance of engines are ever increasing. An equally important requirement is that of reducing the noxious content of the exhaust gas. Doing so, however, results in other problems such as reduced power output and increased fuel consumption.
Conventional products such as compression rings for use in internal combustion engines are typically made of cast iron. However, compression rings made of cast iron which are thin in the axial direction are difficult to manufacture, and those which have a relatively large cross section have a high inertia and are prone to cause a fluttering phenomenon (extraordinary vibration of rings). Another problem with compression rings made of cast iron is that their resistance to wear and heat is not great enough to permit their installation in a position near the top of the piston, which is favorable for the purpose of reducing noxious emissions. Furthermore, the conventional compression rings cannot be mounted on the piston at sufficiently small spacings to prevent the piston from being too heavy to produce a desirably high output power at a higher speed.
The use of compression rings which maintain the airtightness of the combustion chamber greatly improves the service life of an internal combustion engine. While maintaining airtightness, the width of each compression ring in its axial direction must be minimized so as to reduce the area of contact between the ring and the wall of the cylinder, thereby decreasing the frictional loss. At the same time, the weight of the piston must be reduced by using lighter compression rings and by installing them at closer spacings.
In order to meet these requirements, steel piston rings made of Si--Cr steel or 13Cr steel are currently commonly used. Si--Cr steel is inexpensive, but since it does not have great heat collapse and wear resistance, which are two very important properties for piston rings, the entire surface of a piston ring made of this steel species, or at least the upper, lower sides and the sliding surface, should be given a suitable surface treatment. 13Cr steel has a high heat collapse and wear resistance and is mechanically stronger than Si--Cr steel, and a piston ring made of 13Cr steel can be used after treating only the sliding surface. On the other hand, 13Cr steel is more costly.
Accordingly, an object of the present invention is to provide a piston ring member which is free from the defects of a compression ring made of cast iron.
Another object of the present invention is to provide a piston ring member whose cost is between those made of Si--Cr and 13Cr steels but which exhibits properties similar to those made of 13Cr steel.
Still another object is to provide a piston ring member which is easy to manufacture and which allows the internal combustion engine in which it is used to produce a greater output power at a higher speed while maintaining good airtightness of the combustion chamber.